Matsumoto, in U.S. Pat. Nos. 4,164,755 and 4,165,560, discloses a pickup stylus for use with a capacitive information disc and a method for manufacturing the stylus. The stylus is fabricated from a tapered diamond support element having, in the region of its tip, a plurality of conical portions with a common axis. Two of the conical portions are separated by an electrode bearing surface. A record engaging surface is provided in the tip region substantially orthogonal to the electrode bearing surface. The diamond support element includes a pair of converging flat surfaces in the tip region which are disposed such that the intersection of the converging flat surfaces with the record engaging surface defines the side edges of the record engaging surface. The intersection of the converging flat surfaces with a conical portion remote from the electrode bearing surface forms a prow.
The Matsumoto stylus may be manufactured by grinding a conical surface at one end of the diamond element. An electrode bearing surface in the region of the tip and a record engaging surface substantially orthogonal to the electrode bearing surface are formed. A pair of converging substantially flat surfaces are also formed in the region of the tip such that the intersection of the converging flat surfaces with the record engaging surface defines the sides of said record engaging surface.
Keizer, in U.S. Pat. Nos. 4,104,832 and 4,162,510, has disclosed a keel-tipped capacitive information system playback stylus and a method for forming the stylus. The terminating portion of the stylus is shaped to have a prow, a substantially flat rear surface remote from the prow, a pair of substantially parallel side surfaces extending from the side edges of the rear surface, a bottom surface extending from the bottom edge of the rear surface and additional surfaces extending from the prow and intersecting the bottom and side surfaces.
The keel-tipped stylus may be formed with an abrasive lapping disc having a deep, coarse-pitched groove. The tip is fabricated from a tapering support element which is defined at one end by a prow and a substantially flat "V"-shaped rear surface remote from the prow. The lands on the lapping disc lap the shoulders of the stylus. The walls of the abrasive groove form the substantially parallel side surfaces.
I have made a keel-tipped stylus from a support element having a conical tip. The resulting stylus maybe used to recover information from an information track from either a grooved or ungrooved capacitive information disc. In order to obtain the prow and substantially flat "V"-shaped rear surface, I lap an electrode surface and a pair of converging flat surfaces in the tip region which meet to form a point.
I have found that it is difficult to form the pair of converging substantially flat surfaces of substantially the same dimensions such that they meet at the end of the electrode surface. Because of nonuniformities which may occur in the grinding medium, the intersection of the two converging surfaces with the electrode surface may be substantially off-center relative to the stylus axis. This off-center convergence leads to difficulties in forming a record engaging surface.